After the content is used, if the cap is fastened loosely, the sealed state of the interior of the container cannot be maintained, allowing for the entry of air or fungi into the container. As a result, the content becomes oxidized, or molds and the like spread, accelerating the degradation of the content. In order to solve the problem, a cap to be attached to a container opening portion has been proposed. The cap is configured such that, immediately after an appropriate amount of content is used by the user squeezing the body portion of the container to apply an internal pressure to the container, the interior of the container (container opening portion) is sealed without the user operating the cap manually.
For example, Patent Document 1 discloses the following. A cap body fitted on a container opening portion is provided with an ejection passageway communicating with the container opening portion, a base portion, and a check valve. The base portion is fitted in the ejection passageway and includes an ejection hole. The check valve is disposed on the base portion, and only permits the ejection of the content via the ejection hole. The check valve is configured from a cylindrical portion fitted in the ejection passageway, a plurality of elastic pieces that is elastically deformable, and a valve member. The plurality of elastic pieces extends radially from an inner wall surface of the cylindrical portion toward the center, with gaps formed therebetween. The valve member is integrally connected to the distal ends of the elastic pieces, and opens and closes the ejection hole downstream in an ejection direction of the ejection hole. When the internal pressure to the container is removed, the elastic pieces of the check valve recover, whereby the valve member closes the ejection hole to maintain the interior of the container in a sealed state.